[Amps] Ameritron AL-572

[Hal W5GHZ]

Neutralize, do not ground the grids directly.
 
Hal W5GHZ

--- On Sat, 11/6/10, pfizenmayer <pfizenmayer2 at q.com> wrote:


From: pfizenmayer <pfizenmayer2 at q.com>
Subject: Re: [Amps] Ameritron AL-572
To: amps at contesting.com
Date: Saturday, November 6, 2010, 12:25 PM


I have been trying to help a fellow ham get an AL-572 tamed down via emails.

He had a tube short/arc and blow one of the 50 ohms to ground grid 
resistors- the tubes were pretty old and tired anyhow so he bought a matched 
set of 4 572b's from RF Parts.

Replaced the grid resistor - carefully checked all the others and also 
checked all the parasitic choke elements (it has the 4 separate chokes in 
the assembly with the  2 durmica series caps in each resistor leg - all 
components are good )

It is working "OK" on all bands but 15 meters - but on 15 it wants to take 
off .(Whether its VHF or around 21 mhz I dunno)  He has not yet tried to 
re-neutralize. He can get it "operational" by a fairly large change in 
loading  to stop arcing/spitting and at that point its about a 500 watt amp. 
Other bands are an easy KW - (maybe a tad too easy on 10 which makes me 
think its a littel regenerative on 10 and re-neut may be a help)

I have read  , think , all of W8JI's stuff on the AL572 and AL-811 amps and 
not sure of when he said what with respect to directly grounding the grids .

So other than re-neutralizing , what is the current thinking of directly 
grounding the grids ? Anyone know what they are doing as shipped today ? He 
is going to add the gas discharge on the filaments just as a precaution to 
protect his K3 driver, and could easily do the grid grounding at that time ?

What say Ye ?

73 de Hank K7HP 

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